Alloying steels

ABSTRACT

A method of adding an alloying addition, such as lead, to a ferrous metal, by bubbling inert gas, such as argon, through the ferrous metal whilst the metal is contained in a ladle and adding the alloying addition to the turbulent zone created by the passage of the inert gas. The temperature of the ferrous metal in the ladle is maintained above its customary teeming temperature during the adding of the alloying addition. When all the alloying addition has been added the temperature of the metal is allowed to cool to its customary teeming temperature whilst the inert gas is continued to be passed. The ferrous metal is then teemed from the ladle into moulds.

United States Patent [191 Davies et al.

[ Mar. 4, 1975 ALLOYING STEELS [73] Assignee: British Steel Corporation,London,

England [22] Filed: Mar. 15, 1973 [21] Appl. No.: 341,451

Related US. Application Data [63] Continuation of Ser. No. 80,553, Oct.14, 1970,

abandoned.

[30] Foreign Application Priority Data Oct. 15, 1969 Great Britain50609/69 I {52] U.S. Cl. 75/129, 75/130.5 {51] Int. Cl. C22C 33/00 [58]Field of Search 75/129, 130, 130.5, 49,

[56] References Cited UNITED STATES PATENTS 2,915,380 12/1959 Hilty..75/60 3,321,300 5/1967 Worner 75/49 3,545,960 12/1970 McClellan 75/593,547,622 12/1970 Hutchinson 75/49 3,574,603 4/1971 Rassenfoss 75/613,671,224 6/1972 North 75/129 3,672,869 6/1972 Niehaus 75/46 PrimaryExaminer-L. Dewayne Rutledge Assistant Examiner-Peter D. RosenbergAttorney, Agent, or Firm-Bacon & Thomas [57] ABSTRACT A method of addingan alloying addition, such as lead, to a ferrous metal, by bubblinginert gas, such as argon, through the ferrous metal whilst the metal iscontained in a ladle and adding the alloying addition to the turbulentZone created by the passage of the inert gas. The temperature of theferrous metal in the ladle is maintained above its customaryteemingtemperature during the adding of the alloying addition. When allthe alloying addition has been added the temperature of the metal isallowed to cool to its customary teeming temperature whilst the inertgas is continued to be passed. The ferrous metal is then teemed from theladle into moulds.

16 Claims, 3 Drawing Figures PATENTEU 41975 3. 869,283

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PATENTEDHAR 419-75 snmaur PATENTEDMR 1975 SHEET 3 (IF 3 FiQZL.

ALLOYING STEELS This application is a continuation of Ser. No. 80,553,filed Oct. 14, 1970, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the addition to iron and alloys of iron, hereinafter allreferred to as ferrous metals," of an alloying addition, andparticularly an alloying addition for the purpose of improving themachinability of the ferrous metals.

2. Description of Prior Art It is well known to add amachinability-improving alloying addition to ferrous metals, but thealloying addition has in general low or negligible solid solubility inferrous metals so that it is difficult to obtain a good recovery of thealloying addition in the ferrous metal while ensuring that the part ofthe alloying addition which is retained in the ferrous metal is presentin the form of uniformly distributed fine particles.

The presence of large globules of the alloying addition or of a heavysegregation thereof which are commonly found in the bottom of the ingotmeans that a larger part of the bottom of the ingot must be discardedthan the usual discard at the bottom of a rolled ingot.

Furthermore, if the alloying addition is intended to improve themachinability of the ferrous metal, it is important that the alloyingaddition be dispersed as uniformly as possible throughout the ferrousmetal ingot so as to improve the machinability substantially uniformlythroughout the ingot as well as avoiding the Iocalised segregation whichwould be liable to impair the mechanical properties of the ferrousmetal.

Also. the fumes generated when the alloying addition is added to ferrousmetals may be toxic, in which case the fumes may be efficiently removedthroughout the casting process.

The alloying addition may, for example, include one, some or all of theelements lead, selenium and tellurium. in the form of pure metals or inthe form of alloys, or as mineral compounds.

SUMMARY OF THE INVENTION An object of the invention is the provision ofan improved method of adding the alloying addition to ferrous metals,whereby a high recovery of the alloying addition is obtained in theingot and an ingot is produced in which the alloying addition is presentin the form of a uniformly distributed and finely divided micro-dispersion, with a reduction in the segregation of the alloyingaddition as compared with most commonly used methods so that a reducedproportion of the ingot need be discarded.

A further object of the invention is the provision of an improved methodas described above wherein any toxic fumes generated by the alloyingaddition may be efficiently and easily removed.

According to the present invention we provide a method of addingalloying addition to a ferrous metal, the method comprising the stepsof; passing a gas through the ferrous metal, the ferrous metal beingheated to a temperature above its customary teeming temperature, thepassage ofthe gas being such that turbulence is created in the ferrousmetal and a turbulent zone at the surface thereof; simultaneously addingsaid alloying addition to the ferrous metal at or adjacent to theturbulent zone whilst removing any toxic fumes generated; continuing topass the gas through the ferrous metal until the temperature of themetal reaches its customary teeming temperature; and'teemin'g the metalinto moulds whilst removing any toxic fumes generated by the alloyingaddition.

The ferrous metal may be tapped from a furnace into a tapping ladle andthe gas may be passed through the ferrous metal whilst the metal is inthe tapping ladle.

Preferably, the alloying addition is added slowly and in a finelydivided form.

Preferably also, the gas is an inert gas such as argon which will notaffect the composition of the metal.

The term ferrous metal as used herein includes alloy and other steelsand the method of this invention is particularly applicable to ferrousmetals of which the carbon content does not exceed 2.0 percent.

Up to 0.50 percent lead may be added to such ferrous metals.

Lead has negligible solid solubility in steel, but is slightly solublein liquid steel; the solubility of lead increases as the temperature ofthe steel rises.

Steel is normally tapped from the furnace and cast at temperatures asnear its solidifcation temperature as possible since the higher theteeming temperature the more prone is the ingot to defects. It has beenfound if lead is added to the steel during casting, or in the mould, thetemperature of the steel is too low for adequate solubility of the lead,and the ingot tends to contain large globules of lead and to have heavysegregation of lead towards the bottom of the ingot.

Further, the fumes generated when lead is added to steel, are highlytoxic and must be efficiently removed throughout the casting process.

Similar problems are encountered with other alloying additions.

Methods hitherto used for adding a machinability improving alloyingaddition, for example lead, to ferrous metals, for example, plain carbonsteel, have obtained recovery of 15 percent to 64 percent lead in theingot and required approximately 25 percent of the ingot to be discardedbecause segregation of lead particles and normal metallurgical waste.

The use ofthe method of this invention for the addition of lead to asteel can result in a recovery of about percent lead and requires onlythe normal ingot discard to be taken to remove pipe and surface defects.Similar advantageous results are obtained with other alloying elements.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention willnow be described with reference to the accompanying drawings wherein:

FIG. I is a diagrammatic side elevation, partly in section, of a furnaceand ladle for use in carrying out the method of the present invention,

FIG. 2 is a diagrammatic cross-sectional view. to an enlarged scale, ofthe ladle of FIG. 1 showing it in operative position with a fume hood,

FIG. 3 is a diagrammatic cross-sectional view of the apparatus shown inFIG. 2 but with the cross-section taken so as to show the argon inletand pressure gun for adding lead,

FIG. 4 is a view, to an enlarged scale, of the part of FIG. 3 enclosedin the circle marked 4,

the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring firstly to FIG. 1 ofthe drawings, there is shown a conventional electric arc furnace,indicated at 10, pivotally mounted in conventional manner on a base 11.In FIG. 1, the furnace is shown in its tilted position for dischargingits contents into a 60-ton tapping ladle 12 which is suspended, inconventional manner, from an overhead travelling crane, part of the hookof which is shown at 13. The tapping ladle 12 is of conventionalconstruction and is provided with a pouring orifice 14 which can beclosed by a ceramic plug 15 controlled by a mechanical linkage 16.

Referring now to FIGS. 2 and 3 of the drawings, the tapping ladle 12 canbe transported by the overhead crane so that it is positioned in a pit17 formed in the floor 18 of the melting shop.

A steel fume hood 19 lined with a refractory 20 is mounted on an arm 21for pivotal movement about a fixed axis 22 so that the fume hood 19 canbe moved into position to cover the tapping ladle 12 when the ladle ispositioned within the pit 17.

The fume hood 19 is provided with ducting 23 which communicates withfixed ducting 24, when the hood 19 is in its operative position, whichextends to a conventional fume extractor plant illustrateddiagrammatically at 25.

As best shown in FIGS. 3 and 5, means are provided in the base of thetapping ladle 12 for introducing an inert gas. This means comprises aporous brick 26 of generally frusto-conical configuration retained in acorrespondingly shaped refractory retaining formation 27. A flexiblearmoured hose 28 extends from an argon supply to the undersurface of theporous brick 26 and suitable connecting means are provided between thehose and the brick so that the hose can be connected to the brick whenthe ladle is positioned in the pit 17.

An aperture 29 is formed in the fume hood 19 to enable a conventionalpressure gun 30 to be introduced into the ladle. The pressure gun is ofconventional construction and includes a pressurised hopper 31 and anozzle 32 in the form of an open-ended funnel with a solid central cone.Air under pressure is applied to the hopper 31 so as to force lead shotfrom the hopper to the nozzle 32, which is arranged to disperse thestream of lead particles into a spray.

Referring now particularly to FIG. 6 of the drawings, the tapping ladle12, after the introduction of lead, can be raised by the overhead craneout of the pit 17, and transported until its discharge orifice 14 ispositioned over the ingate of a set of eight ingot moulds 33 arrangedfor bottom casting in conventional manner.

Movable ducting 34 is provided to cover the eight ingot moulds and theingate. The ducting 34 extends to fixed ducting 35 which leads to aconventional fume extractor plant.

By way of example, the addition of lead to a low alloy steel using theabove apparatus will now be described. In this example the followingprocedure was carried out.

The steel of the present example made in the electric arc furnace 10 wasa low alloy steel having a furnace analysis as set out below:

Iron and usual impurities balance The steel was tapped from the furnace10 by tilting the furnace to the position shown in FIG. 1 so that thesteel issued in the stream 39 and entered the 60-ton tapping ladle 12 ata temperature of 1 680C, that is approximately C above its customarytapping temperature.

When the tapping ladle 12 was filled the furnace 10 was returned to itsupright position and the ladle 12 was lifted and transported by theoverhead crane until it was positioned in the pit 17, as shown in FIGS.2 and 3. The flexible armoured hose 28 was then connected to the porousbrick 26, the fume hood 19 was pivoted about its axis 22 into operativeposition over the ladle 12, as shown in FIGS. 2 and 3, and the pressuregun 30 was introduced through the aperture 29 in the fume hood 19.

Argon gas was then bubbled through the steel at a pressure ofapproximately to p.s.i. at a flow rate of between 20 to 25 cubic feetper minute.

The introduction of the argon created turbulence in the steel and aturbulent zone 36 at the surface 37 of the steel.

Whilst the argon was being passed a spray of finely divided leadparticles was introduced into the steel adjacent to the turbulent zones36 by the pressure gun 30. The fume extractor plant 25 was operated toremove the toxic fumes generated by the lead on addition of the lead tothe steel. A total weight of 330 lbs of lead was added as slowly aspossible over a period of 15 to 20 minutes and the argon was passedcontinuously.

The high temperature of the steel ensured the solution of the leadaddition and the turbulence created in the steel by the argon and theslow addition of the lead particles ensured the uniform distribution ofthe lead and prevented the segregation of the lead and the formation oflead globules.

When all the lead had been added passage of the argon was continueduntil the temperature of the steel had reached its customary teemingtemperature of l,570C.

The fume hood 19 was pivoted about its axis 22 out of operative positionwith the ladle 12 and then the overhead crane was engaged with the ladlel2 and the ladle was lifted and transported to a further position whereits discharge orifice 14 was positioned above the ingate of the ingotmoulds 33, as shown in FIG. 6.

The linkage 16 was then operated to lift the ceramic plug 15 and soenable the steel in the ladle 12 to leave the discharge orifice 14 in astream 38 and enter the ingate of the ingot moulds 33 in conventionalmanner. During this operation the movable ducting 34 was positioned overthe ingot moulds and ingate, as shown in FIG. 6, and the fume extractorplant was operated to move any further toxic fumes given off during thecasting operation.

The additional turbulence created by teeming also helped to ensureuniform distribution of the lead.

The ingots produced were tested to determine the lead distribution andcontent. The tests performed were as follows.

A photographic paper was soaked for 2 minutes in 5 percent sodiumhydroxide solution and was placed on a coarsely ground cross-section ofa billet product of the ingot. The paper was left for 3 minutes and thenplaced in 5 percent sodium sulphite solution, the prints were thenwashed and dried.

On examination, the lead distribution shows on the paper as a brownspeckled pattern, the intensity of the pattern indicating thedistribution.

In a second test a short piece of the billet was sawn and placed in asmall furnace at a minimum temperature of 600C. Any lead particles onthe surface of the billet melt and exude, forming droplets on the billetsurface. The sample was then cooled and the droplets examined. Thepresence of droplets gives an indication of large particles present inthe sample.

In a third test, a short piece of sawn billet was held in a shapingmachine and cuttings were taken from the whole cross-section of thebillet. The lead content of the cuttings was then determined chemicallyin conventional manner.

In a fourth test billets obtained from the ingot were testedultrasonically. The ultrasonic beam passed through the cross-section ofthe billet and a signal was recorded on an oscilloscope by the returningsound beam reflected from the opposite base of the billet. Anyinterference with this beam by large lead particles given an alteredsignal on the oscilloscope.

We have found in commercial production that it is convenient to carryout the last mentioned test on all the billets produced according to themethod of the present invention as a routine quality control test whilstthe first three tests described above are conducted on random samplestaken from different ingot positions as is considered appropriate duringa production run.

In the case of the example described above, it was found that the ingotswhich were produced had an average lead content of 0.18 percentindicating that 70 percent of the lead had been recovered in the ingot.It was also found that substantially all of the lead was uniformlydistributed as a finely divided micro-dispersion and it was found to beunnecessary to discard any part of an ingot due to gross segregation oflead particles, although the normal casting discard had still to bemade.

In the example above described the ferrous metal was heated to the abovementioned temperature above its customary tapping temperature bysuperheating the ferrous metal in the furnace before tapping the furnaceinto the ladle. In this case, the argon case may be at or near roomtemperature.

Alternatively, the gas may be heated to a temperature such that thetemperature of the superheated ferrous metal is maintained at atemperature above its customary tapping temperature, i.e., 1,610C whilstit is in the ladle.

Still further alternatively, it is proposed that the ferrous metal maybe heated to a temperature above its customary tapping temperature bypassing gas through the ferrous metal in the ladle, the gas having beenheated to a temperature sufficiently high to cause the ferrous metal toreach this temperature.

In such cases where the temperature of the gas is above roomtemperature, after introduction of the lead, the temperature of the gasis reduced to or near room temperature to enable the temperature of themetal to reach its customary teeming temperature.

Although argon has been described herein as the gas passed into thesteel to create the turbulence, other inert gases may be used if desiredso long as the inert gas used does not affect the properties of thesteel in an undesirable manner.

Although the addition of lead has been described hereinbefore in theexample given other alloying additions such as selenium and tellurium,either alone or in combination may be added to a ferrous metal toimprove its machineability by the method of the present invention and ifdesired other alloying additions may also be added to a ferrous metalusing the method of the present invention.

Instead of using a pressure gun to add the alloying addition thealloying addition may be added by any other of the known means which areavailable in the art, for example, by means of gravity feed from ahopper.

In this specification all compositions are expressed in percentage byweight.

If desired the inert gas may be introduced into the ladle through morethan one porous brick.

We claim:

1. A method of adding an alloying addition to a par ticular steel, themethod comprising the steps of heating the steel in a furnace to atemperature substantially above that at which said particular steel isnormally heated for tapping into a ladle for teeming into ingot molds,tapping the steel from the furnace into a ladle while it is at atemperature substantially above that at which it is customarily tappedfrom the furnace for teeming into ingot molds, passing gas through thesteel in the ladle, the passage of gas being such that turbulence iscreated in the steel and a turbulent zone is created at the surfacethereof, simultaneously adding said alloying addition to the steel inthe region of said turbulent zone while said steel is at a temperaturesufficient to ensure solution of said alloying addition, removing anytoxic fumes generated by the alloying addition, continuing to pass gasthrough the steel so as to maintain turbulence therein and permittingthe steel to cool until the temperature thereof reaches the customaryteeming temperature for said particular steel, and teeming the steelinto molds.

2. A method according to claim 1, wherein the alloying addition is addedslowly and in finely divided form.

3. A method according to claim 1, wherein the gas in an inert gas whichdoes not affect the composition of the metal.

4. A method according to claim 3, wherein the gas is argon.

5. A method according to claim 1, wherein the steel includes a carboncontent not in excess of 2.0 percent.

6. A method according to claim 1, wherein the alloying addition is lead.

7. A method according to claim 1, wherein the alloying addition is leadand up to 0.5 percent lead is added.

8. A method according to claim 1, wherein the gas is introduced into thesteel at substantially room temperature.

9. A method according to claim 1, wherein the gas is introduced into thesteel at an elevated temperature so asto maintain the steel at atemperature above its customary tapping temperature sufficient to ensuresolution of said alloying addition.

10. A method according to claim 1, wherein the gas is introduced intothe steel at a temperature sufficiently high to raise the temperature ofthe steel to a temperature above its customary tapping temperaturesufficient to ensure solution of said alloying addition.

11. A method according to claim 9, wherein the temperature of the gas isreduced to room temperature or to substantially room temperature afteraddition of the alloying addition to enable the temperature of the steelto cool to its customary teeming temperature.

12. A method according to claim 10, wherein the temperature of the gasis reduced to room temperature or to substantially room temperatureafter addition of the alloying addition to enable the temperature of thesteel to cool to its customary teeming temperature.

13. A method according to claim 1, wherein the gas is introduced intothe ladle at the bottom thereof.

14. A method according to claim 1, wherein said customary tappingtemperature is l,610C.

15. A method according to claim 1, wherein the steel is heated to atemperature of about 1,680C.

16. A method of adding'lead to steel to assure a uniform distribution oflead particles finely divided as a micro-dispersion in the steel whensolidified, including the steps of containing molten steel to which leadis to be added in a vessel at a temperature above its customary tappingtemperature, adding enough lead to the steel to obtain a lead contentsubstantially equal to the solubility limit under existing processconditions, retaining the steel within the vessel for a time after thelead is added and permitting it to cool until the steel is at itscustomary teeming temperature, removing steel containing leadessentially only in the dissolved state from the vessel and solidifyingthe steel removed from the vessel.

1. A METHOD OF ADDING AN ALLOYING ADDITION TO A PARTICULAR STEEL, THEMETHOD COMPRISING THE STEPS OF HEATING THE STEEL IN A FURNACE TO ATEMPERATURE SUBSTANTIALLY ABOVE THAT AT WHICH SAID PARTICULAR STEEL ISNORMALLY HEATED FOR TAPPING INTO A LADLE FOR TEEMING INTO INGOT MOLDS,TAPPING THE STEEL FROM THE FURNACE INTO A LADEL WHILE IT IS ATEMPERATURE SUBSTANTIALLY ABOVE THAT AT WHICH IT IS CUMSTOMARILY TAPPEDFROM THE FURNACE FOR TEEMING INTO INGOT MOLDS, PASSING GASS THROUGH THESTEEL IN THE LADEL, THE PASSAGE OF GAS BEING SUCH THAT TURBULENCE ISCREATED IN THE STEEL AND A TURBULENT ZONE IS CREATED AT THE SURFACETHEREOF, SIMULTANEOUSLY ADDING SAID ALLOYING ADDITION TO THE STEEL INTHE REGION OF SAID TURBULENT ZONE WHILE SAID STEEL IS AT A TEMPERATURESUFFICIENT TO ENSURE SOLUTION OF SAID ALLOYING ADDITION, REMOVING ANYTOXIC FUMES GENERATED BY THE ALLOYING ADDITION, CONTINUING TO PASS GASTHROUGH THE STEEL SO AS TO MAINTAIN TURBULENCE THEREIN AND PERMITTINGTHE STEEL TO COOL UNTIL THE TEMPERATURE THEREOF REACHES THE CUSTOMARYTEEMING TEMPERATURE FOR SAID PARTICULAR STEEL, AND TEEMING THE STEELINTO MOLDS.
 2. A method according to claim 1, wherein the alloyingaddition is added slowly and in finely divided form.
 3. A methodaccording to claim 1, wherein the gas in an inert gas which does notaffect the composition of the metal.
 4. A method according to claim 3,wherein the gas is argon.
 5. A method according to claim 1, wherein thesteel includes a carbon content not in excess of 2.0 percent.
 6. Amethod according to claim 1, wherein the alloying addition is lead.
 7. Amethod according to claim 1, wherein the alloying addition is lead andup to 0.5 percent lead is added.
 8. A method according to claim 1,wherein the gas is introduced into the steel at substantially roomtemperature.
 9. A method according to claim 1, wherein the gas isintroduced into the steel at an elevated temperature so as to maintainthe steel at a temperature above its customary tapping temperaturesufficient to ensure solution of said alloying addition.
 10. A methodaccording to claim 1, wherein the gas is introduced into the steel at atemperature sufficiently high to raise the temperature of the steel to atemperature above its customary tapping temperature sufficient to ensuresolution of said alloying addition.
 11. A method according to claim 9,wherein the temperature of the gas is reduced to room temperature or tosubstantially room temperature after addition of the alloying additionto enable the temperature of the steel to cool to its customary teemingtemperature.
 12. A method according to claim 10, wherein the temperatureof the gas is reduced to room temperature or to substantially roomtemperature after addition of the alloying addition to enable thetemperature of the steel to cool to its customary teeming temperature.13. A method according to claim 1, wherein the gas is introduced intothe ladle at the bottom thereof.
 14. A method according to claim 1,wherein said customary tapping temperature is 1,610*C.
 15. A methodaccording to claim 1, wherein the steel is heated to a temperature ofabout 1,680*C.
 16. A method of adding lead to steel to assure a uniformdistribution of lead particles finely divided as a micro-dispersion inthe steel when solidified, including the steps of containing moltensteel to which lead is to be added in a vessel at a temperature aboveits customary tapping temperature, adding enough lead to the steel toobtain a lead content substantially equal to the solubility limit underexisting process conditions, retaining the steel within the vessel for atime after the lead is added and permitting it to cool until the steelis at its customary teeming temperature, removing steel containing leadessentially only in the dissolved state from the vessel and solidifyingthe steel removed from the vessel.